First, back off and put down the rope. There really is fun theory for guitar. Almost everyone turns off when the word theory trots out, but that's really too bad. Why?
Because theory isn't dry-as-dust useless. It's just that most of us have had some teachers that were! Theory rocks! For example:
When you run your thumb over the strings of your first open tuning, if you have any soul at all your heart is going to swell. Those sounds, that chord, that arpeggio you just played is built on theory. Did that hurt? C'mon you big baby .... stay with me.
When you play your first song, whether it's a favorite folk, blues, calypso, pop or country tune from a musician you admire .... or one of your own .... likely it will be built on a I-IV-V progression. It will sound amazing to you. Here's why.
Most music is built on tension and release. I hope your home is pleasant .... that's where you spend a lot of your time. In music, home's your I chord. Most songs start and end there. Vacations add pleasure to life .... your IV and V chords. (hope this analogy's workin'. I've never had a bad vacation, but I have friends who never seem to have a good one.)
Anyhow, IV and V chords set up a pleasant tension. They seek release to the I chord. It's good to go on a great trip, but it's also good to come home .... the satisfying I chord release.
For a great example of this interplay listen to Kenny Rogers' "The Gambler". See if you can pick out the times it slips back and forth from "vacation" to "home". It's a good exercise.
The I-IV-V progression comes from the scale of any key you're playing. In the key of C the scale starts at C and goes D E F G A B and then C ....one octave (from Latin octo) the eighth note from where you started.
See that F in the scale? Counting from C it's four notes away. When you play in C Major (no sharps or flats - # or b), F is the root of the IV chord in the I-IV-V progression. Armed with this fun theory for guitar, I bet you've figured out what the root note is for the V chord. Yes, it's G.
While we're at it, what is a chord anyway? Three or more notes that sound good together. There's lots of technical definitions, but that's what it comes down to. Sometimes you'll see references to two-note chords, especially in slide guitar. Well, sort of true .... but those are really called double stops in guitar lingo.
Kenny Rogers sings "The Gambler" in the key of E .... at least he starts it that way .... then it modulates (moves to another key) to F.
How does that relate to fun theory for guitar? First, I've never met anyone who didn't tap their foot to this great tune. Even some of my jazz-snob friends who grudgingly admit this is a great song. The I-IV-V makes it possible. Without it --- no tune!
Put your guitar in Open D tuning and capo on the 2nd fret, put Kenny on YouTube .... live version preferably for this tune .... and play along!